The present invention relates to a new and improved construction of a gas-blast switch.
Generally speaking, the gas-blast switch of the present development is of the type containing a movable, substantially tubular-shaped and displaceable contact element or piece which is guided by a partition or separation wall which subdivides the internal space or compartment of the switch housing into an extinguishing chamber and an expansion chamber. By means of the contact element, during the course of a cut-off stroke, there can be established a current connection between both of these chambers. There is also provided a stationary contact set arranged in the extinguishing chamber or compartment and coacting with the movable contact element. The contact set, in turn, contains a rim of rated current contacts which, in the cut-on position, engages about the movable contact element. Further, there is provided a burn-off ring which is electrically connected with the rated current contacts and an intermediate electrode which is electrically insulated from the rated current contacts. The intermediate electrode in the cut-on position sealingly engages into the movable contact element, and such during the course of the cut-off stroke initially comes out of engagement with the rated current contacts and only afterwards comes out of engagement with the intermediate electrode, so that initially an arc is drawn between the burn-off ring and the intermediate electrode.
Such type of gas-blast switches are typically, although not exclusively, used for intermediate voltages in a range of 1-36 kV.
With heretofore known switches of this type there does not exist any adequate assurance that the arc which is drawn between the burn-off ring and the intermediate electrode will not commutate back from the burn-off ring to the rated current contacts, as soon as the movable contact element has departed from the intermediate electrode, and thus, has released the flow connection from the extinguishing chamber or compartment to the expansion chamber or compartment.
Additionally, the heretofore known gas-blast switches likewise afford little assurance, in particular during the cut-off of comparatively low currents, that there will be a rapid extinguishing of the switching arc, since the pressure build-up produced by the switching arc in this case is too low in order to ensure for an uninterrupted outflow of the heated gas through the movable contact element, and thus, to equally ensure for the blowing of the switching arc by inflowing extinguishing gas.